There are already known a conversation of users present in spaces remote from each other while viewing images of their opposite parties by means of communication technology, and an image display system for realizing such conversation. In this system, image data when the image of one user is taken is transmitted, and the image data is received and expanded on the side of the other users. Thus, the image of the user on the one side is displayed on a display screen of the opposite user. As a result, the user viewing the display screen feels that as if the user were facing the conversation partner.
Moreover, in recent years, technologies of changing, when the position of the view point of a user viewing a display screen changes, an image displayed on the display screen changes in association with the change in the position (refer to JP 2012-85159A and JP 2014-71871A). Specifically, with image display systems described in JP 2012-85159A and JP 2014-71871A (referred to as image communication systems in JP 2012-85159A and JP 2014-71871A), when the user viewing the displayed image moves rightward/leftward, the displayed image switches so as to rotate about a vertical axis as shown in FIG. 14. As a result, the image displayed on the display screen becomes an image having a left portion and a right portion different in a depth distance as shown in FIG. 14. FIG. 14 shows a state where the image changes in association with the movement of the user viewing the display screen in the conventional image display systems (specifically, the image display systems described in JP 2012-85159A and JP 2014-71871A).
As described before, with the image display systems described in JP 2012-85159A and JP 2014-71871A, the depths of portions of the displayed image are changed in response to the movement (movement in the right/left direction) of the view point position of the user viewing the display screen, thereby reproducing an image in a space of the conversation partner viewed from the view point position after the movement.
Incidentally, when the image on the display screen is changed in response to the movement of the view point position of the person viewing the display screen, such processing as modifying the image before the movement of the view point position and the like is necessary. It is surely preferred to carry out this modification processing in a simpler procedure. On the other hand, the image display systems according to JP 2012-85159A and JP 2014-71871A extract an image of a person from the image, apply predetermined processing to the person image, and combine the processed person image and a background image with each other to form the displayed image. In other words, in the image display systems according to JP 2012-85159A and JP 2014-71871A, when the image on the display screen is to be changed in response to the movement of the view point position of the person viewing the display screen, the extraction of the person image is essential, and time is accordingly required for the processing.
Moreover, in the image display systems described in JP 2012-85159A and JP 2014-71871A, the displayed image switches so as to rotate about the vertical axis when the user viewing the display screen moves rightward/leftward as described before. However, when one conversing person out of the persons who are actually facing each other for the conversation moves rightward/leftward, the other conversing person whom the one conversing person is viewing does not rotate as described before, but only horizontally moves.
Further, when the displayed image is changed in response to the movement of the view point position of the user viewing the display screen, it is necessary to consider a difference in the position in a depth direction between the image of the person and the image of the background. However, the image display systems described in JP 2012-85159A and JP 2014-71871A rotate both the image of the person and the image of the background by the same rotation amount (rotation angle) when the user viewing the display screen moves rightward/leftward. Therefore, in the image display systems described in JP 2012-85159A and JP 2014-71871A, the image of the conversation partner when the user viewing the display screen moves rightward/leftward is different from an appearance of the conversation partner when the user actually faces and views the conversation partner (namely, a figure of the conversation partner recognized by the user through the own sense of vision).
Furthermore, in the image display systems according to JP 2012-85159A and JP 2014-71871A, a display size of the image of the conversation partner changes in accordance with the distance (depth distance) of the conversation partner as shown in FIG. 15. Specifically, the display size is optically determined in accordance with characteristics of an imaging device (specifically, characteristics of lenses) for imaging the conversation partner. Therefore, the conversation partner appears in a smaller size in the image as the depth distance of the conversation partner increases (in other words, the conversation partner separates more from the imaging device) as shown in FIG. 15. FIG. 15 shows a state where the image of the conversation partner is displayed in the display size determined in accordance with the depth distance of the conversation partner in the conventional image display systems (specifically, the image display systems described in JP 2012-85159A and JP 2014-71871A).
However, when one conversing person out of the persons actually conversing each other moves in the depth direction, the appearance (size) of the figure of the one conversing person viewed by the other conversing person is felt not to change through the human vision. Therefore, in the image display systems according to JP 2012-85159A and JP 2014-71871A, the display size of the image of the conversation partner when the depth distance changes is different from the size felt when the user actually faces and views the conversation partner (namely, the size of the conversation partner recognized by the user through the own sense of vision).